1. Field of the Invention
Having a photodetector that contains a highly efficient multiplication layer, such as silicon, coupled to a highly efficient absorption region, such as indium gallium arsenide, is a large advance in the field of electronics. This invention relates in general to a method of making a semiconductor device. The invention uses silicon as the multiplication region of a photodetector in a number of photodetector structures. Further, the invention integrates photodetectors with other electronic devices to make more complex electronic components and systems.
2. Description of Related Art
The use of semiconductor materials to create various electronic devices is largely dependent on the requirements of the device for a given task, the ability to use certain materials together in a given device, and the cost for the finished device. As device requirements are tightened or increased, new methods and materials combinations are required to meet the requirements for the device.
An avalanche photodetector (APD) has two functions: the absorption and conversion of light to an electrical signal, and the amplification of that electrical signal through avalanche multiplication. These functions can be done by a single material, such as silicon, or by two materials grown epitaxially, one for the absorption and another for the multiplication. The performance of an APD is based on the achievable signal processing speed and noise, which are dependent on the absorption and multiplication efficiencies. These parameters are expressed by the responsivity, the 3-dB frequency bandwidth, and the excess noise factor. The excess noise factor and 3-dB bandwidth are dependent on the total device thickness and the ratio between electron and hole ionization coefficients of the material used for multiplication. The larger the ratio between the electron and hole ionization coefficients, the larger the gain bandwidth product of the APD will be. Further, the larger the coefficient ratio, the less noisy the APD will be.
Current devices that have tried to maximize detector performance have fallen short of desired efficiencies due to the trade off between absorption coefficient and electron/hole ionization coefficients. Materials, such as silicon, that have high electron/hole ionization coefficient ratios do not have good absorption in the desired optical regions, such as the telecommunications wavelengths of 1.3 and 1.5 xcexcm. Materials that have good absorption do not have a high ionization coefficient ratio. Heterojunction devices have, until now, been limited to lattice matched materials, and device efficiencies have not been significantly increased through the use of heterojunction APDs because of the lattice matching limitation.
It can be seen then that there is a need for a method of making an APD that has high efficiency. It can also be seen that there is a need for a method of making an APD that has a high electron to hole ionization ratio in the multiplication region and a high absorption region for converting light into electricity. It can also be seen that there is a need for a device that can absorb light in the desired optical regions and efficiently and precisely convert that light into electrical signals.
To minimize the limitations in the prior art described above, and to minimize other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a powerful and highly productive apparatus and method for making APDs. The present invention is comprehensive and is fully integrable with present fabrication methods.
The present invention solves the above-described problems by providing a method for fusing high ionization ratio materials with high efficiency absorption materials. One material is used as an absorption region for converting light into an electronic signal while another material is used for the amplification region. Silicon is the material of choice for the amplification, or multiplication region, as the properties of silicon are superior for this task. The method is easily performed and is relatively inexpensive. Further, the method provides for customization of semiconductor devices by bandwidth by choosing the absorption material. Since lattice matching is no longer required, the multiplication and absorption regions can be selected separately to optimize the final device.
One object of the present invention is to provide a method for making high efficiency avalanche photodetectors. Another object of the present invention is to provide a avalanche photodetector with a high ionization rate material in contact with a highly efficient absorption material.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there is illustrated and described specific examples of the method and product in accordance with the invention.